<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>polka-dot-pattern</title>
    <style>
        .polka-dot {
            width: 240px;
            height: 240px;
            background-color: #000;
            background-image: radial-gradient(#fff 10%,transparent 11%),radial-gradient(#fff 10%, transparent 11%);
            background-size: 60px 60px;
            background-position: 0 0,30px 30px;
            background-repeat: repeat;
        }
    </style>
</head>
<body>
    <div class="polka-dot"></div>
</body>
</html>